1. Field of the Invention
The present invention relates to a method for blank pressing a glass body, especially for an optical application, using a press mold comprising an upper mold part and a lower mold part and/or a ring, this press mold receiving the glass body heated above a shaping temperature. It also relates to an apparatus for performing this method.
The term “blank pressing” means pressing a glass body having optically active surfaces, so that these surfaces do not need to be worked further. Polishing and grinding steps are eliminated for these surfaces.
2. Description of the Related Art
JP 225 26 29 describes methods of this type, in which the glass body is processed in a two-step pressing process and the already shaped glass body is cooled during the pressing process. In a preferred embodiment a cylindrical perform is placed between the upper and lower dies, heated and subsequently shaped by pressing. After finishing the first molding or shaping process the pressing force is temporarily completely or partially reduced and then applied again during the cooling down below the glass transition temperature TG.
U.S. Pat. No. 5,987,922 discloses a manufacturing method for a melted glass body, which is useable in optical equipment, for example as a lens. In this known method first an initial pressing force is applied to the viscous glass body, which is superimposed by an intermediate pressure after a time interval of, for example, 5 to 20 seconds. The intermediate pressure decreases with decreasing glass temperature.
The essential disadvantage of the currently known methods is that blank-pressed optical components, especially with large diameters, cannot be efficiently made with the required quality.